Not all synthetics are the same.

If you use Mobil 1 5-30 you will probably have a slight drop in oil pressure due to it's viscosity.

If you can find it, I'd reccomend the Mobil 1 0-40, I've switched my LT1 to this and now have slightly higher hot oil pressure.


Your problem is most likely related to your idle. You need a tune to get your idle right and to make sure that your mixture is correct and you aren't washing down the cylinder walls with unburnt fuel.